The present invention relates to the field of vaccine compositions. More especially, the invention relates to new adjuvants used for increasing the immunogenicity of vaccine compositions.
There are a large number of antigens which, when injected into animals, will cause a production of antibodies which are specific to them. One of the principles of vaccination is to stimulate antibody production by the body of a man or an animal by administering chosen antigens thereto. The antibodies thus produced will then enable the body to defend itself against a subsequent infection. However, some antigens do not bring about sufficient stimulation of the immune system when they are administered alone. Hence an adjuvant which will enable the body""s immune response to be increased has to be added to them in order to obtain a sufficient amount of antibody to be protective.
Among known adjuvants, aluminium hydroxide and aluminium phosphate, which are customarily used in human vaccines, may be mentioned. However, these compounds do not possess an adjuvant property with respect to all antigens. In particular, they do not enable the immunogenicity of influenza vaccine to be increased.
There is hence a need to be able to have adjuvants at one""s disposal which enable the immunogenicity of the antigens administered in a vaccine composition to be increased, without any risk of toxicity.
In addition, it is advantageous to have adjuvants at one""s disposal which are capable of inducing an immune response that manifests itself in a production of secretory antibodies, such as IgAs.
To this end, the invention provides for the use of an amphipathic compound comprising a lipophilic group derived from a sterol linked to a cationic group, for the production of a vaccine composition.
A subject of the invention is also the use of such an amphipathic compound as adjuvant in the administration of a vaccine.
A subject of the invention is also a vaccine composition comprising at least one antigen, characterized in that it comprises, in addition, at least one amphipathic compound possessing a lipophilic group derived from a sterol linked to a cationic group.
A further subject of the invention is a product containing at least one antigen and one amphipathic compound comprising a lipophilic group derived from a sterol linked to a cationic group, as a combination product for use simultaneously, separately or staggered over time in vaccination.
Another subject of the invention is a method for inducing an immune response in a mammal, consisting in administering at least one antigen to the mammal, characterized in that it consists in administering, in addition, at least one amphipathic compound comprising a lipophilic group derived from a sterol linked to a cationic group.
For the purposes of the present invention, the term amphipathic denotes a compound which possesses both a hydrophobic portion and a hydrophilic portion.
Among sterol derivatives capable of yielding the compounds according to the invention, cholesterol, phytosterol and ergosterol may be mentioned. Cholesterol derivatives are especially suitable.
The cationic group of the amphipathic compounds according to the invention can consist of a quaternary ammonium or an amine which can be protonated.
The lipophilic group is attached to the cationic group by means of an ester, ether, amide or carbamoyl link, among which ester, amide and carbamoyl links have the advantage that they can be hydrolysed in the cell.
The linkage between the 2 groups is preferably effected via a spacer arm consisting of a branched or unbranched alkyl chain comprising from 1 to 20 carbon atoms.
Among the compounds suitable for the purposes of the invention, there may be mentioned those mentioned in U.S. Pat. No. 5,283,185 and, in particular:
cholesteryl-3xcex2-carboxamidoethylenetrimethyl-ammonium iodide,
cholesteryl-3xcex2-carboxamidoethylenamine,
cholesteryl-3xcex2-oxysuccinamidoethylene-trimethylammonium iodide,
3xcex2-[N-(Nxe2x80x2,Nxe2x80x2-dimethylaminoethane)carbamoyl]-cholesterol,
3xcex2-[N-(polyethylenimine)carbamoyl]cholesterol among which 3xcex2-[N-(Nxe2x80x2,Nxe2x80x2-dimethylaminoethane)carbamoyl]cholesterol is especially advantageous.
The amphipathic compounds according to the invention may be obtained by condensation between a sterol derivative and a compound containing a cationic group, according to one of the methods described in xe2x80x9cAdvanced Organic Chemistryxe2x80x9d Part B: Reactions and Synthesis (F. A. Carey and R. J. Sundbergxe2x80x94Plenum Publishing Corp.). More especially, some of the compounds according to the invention may be prepared according to the methods described in U.S. Pat. No. 5,283,185.
The amphipathic compounds obtained in alcoholic solution can then be dispersed in water or in an aqueous buffer, and can yield a suspension of micelles or of liposomes. Advantageously, the amphipathic compounds of the invention are combined with a neutral lipid such as a phospholipid, for example dioleoylphosphatidylethanol-amine (DOPE) or dioleoylphosphatidylcholine (DOPC). This combination causes the amphipathic compounds according to the invention to organize themselves in the form of liposomes rather than micelles during the phase of dispersion in an aqueous environment. The molar proportion of neutral lipid combined with the amphipathic compounds is preferably greater than 20%.
The products obtained according to the invention did not give rise to any acute toxicity reaction when they were inoculated into mice.
The antigen used to induce a protective immune response consists of any antigen customarily used in a vaccine composition, either alone or in combination with another antigen.
In particular, the amphipathic compounds according to the invention prove to be good immunoadjuvants when they are combined with the influenza virus vaccine comprising, in particular: the HA protein which is a haemagglutinin located at the surface of the influenza virus envelope, the NP protein which is a capsid nucleoprotein linked to the viral RNA and an M protein or protein xe2x80x9cmatrixxe2x80x9d of the envelope.
Combination between the antigen whose immunogenicity it is desired to increase and the micellar or liposomal suspension of amphipathic compounds takes place spontaneously by hydrophobic and electrostatic interaction on mixing the constituents.
The vaccine compositions obtained possess good stability. However, the liposomal suspension appears preferable to the micellar suspension.
In addition, the liposomal suspension can be sterilized by filtration and lyophilized.
It is obvious that it is possible to add ingredients traditionally used in vaccines, such as water, physiological saline or a buffer substance, to the vaccine compositions obtained.
Administration of the vaccine compositions obtained according to the invention may be performed by all the routes customarily used for the administration of vaccines, and in particular by the subcutaneous or intranasal route. It is also possible to choose a different route for the primary immunization and the booster immunization.
It is possible to administer separately the composition comprising the antigen and the composition containing the amphipathic compounds according to the invention; however, the administration of a liposomal composition of amphipathic compounds according to the invention combined with the antigen makes it possible not only to increase the humoral type immune response, but also to induce specific cytotoxic T lymphocytes.
A better understanding of the invention will be gained on reading the non-limiting examples which follow, reference being made to the figures.